The present disclosure relates to a control device for a robot that is configured of link structures, a control method and a computer program, specifically relates to a control device for a robot having unactuated joints where a portion of the joints does not exert a driving force, a control method and a computer program.
An inverted pendulum-type robot or biped walking type robot has superior characteristics in that, since a ground contact area thereof is small, the robot hardly interferes with people when coexisting with people, and the robot able to provide various services to people. Conversely, this type of robot has a problem in which, as the ground contact area is small, in order to perform a task there are strict restraints on external forces that are obtained from the environment. In the inverted pendulum-type robot, a supporting point moment of rotation may not be obtained and in the biped walking type robot, an inequality constraint is added to the moment that is obtained from a road surface according to the shape of the sole of the foot thereof. As a further extreme example, a space robot is exemplified. It is difficult the space robot to obtain absolutely a reaction from the environment. These robots have a portion of the joints being incapable of exerting force and the joints being incapable of modeling as unactuated joints.
An example of joint configuration of the robot having unactuated joints is illustrated in FIG. 11 to 13. FIG. 11 shows a joint configuration example of an inverted pendulum-type robot. The translational movement component of a wheel is expressed as a prismatic joint, and a posture change of the entire robot using a wheel is expressed as a rotational joint continuously connected to the next. Because the entire robot may be rotated freely with a point rotation, the joints are expressed as unactuated joints. The remaining joints are arm joints, and are all actuated joints. In addition, FIG. 12 shows a joint configuration example of a biped walking type robot. The rotational joints of the leg are all actuated joints, and, additional to that, and have six degrees of freedom made up of three translational degrees of freedom and three rotational degrees of freedom, in order that the entire robot may freely express movement in a space. These six degrees of freedom are virtual or theoretical joints, and, as they are non-existent, are not able to exert force. Accordingly, they are expressed as unactuated joints. The biped walking type robot is modeled as a system having unactuated joints with six degrees of freedom, however the whole body may be controlled using a force and a moment obtained from the foot. In addition, FIG. 13 shows a joint configuration example of a space robot. The joints of the robot arm that is mounted on the space robot are expressed as actuated joints. However, the three translational degrees of freedom and the three rotational degrees of freedom of the entire robot are expressed as the six degrees of freedom of the unactuated joints. The space robot, unlike a biped walking type robot, is not able to obtain an external force.
In a link structure, such as in a robot, for example, it is necessary that the joint velocity be obtained, in order to generate a desired speed position of the end of the hand. Otherwise, it is necessary that a joint force be obtained in order to generate a desired acceleration. In a system that is configured only of actuated joints, all the components of joint velocity, or all the components of joint acceleration may be controlled. However, in a system which includes unactuated joints, there is a problem that components of the unactuated joints may not be controlled.
As an important concept in the robot control of the force control system, a space that describes the relation between a force that acts on the robot and a generated acceleration, in other words, an operational space, is exemplified. For example, the position of tip of the hand of the robot is defined as the operational space, and the operational space is used to determine the joint force for generating a desired acceleration at the hand tip. Various methods for precisely controlling the acceleration of the operational space have been suggested (for example, Japanese Unexamined Patent Application Publication Nos. 2009-95959 and 2010-188471), however the object in any of these methods is limited to a case where all the joints are actuated joints.